That is an awfully rude reaction to someone else's work. I don't even know if SilverVortex is on the dev team for this or not, but if he is, then its him and the rest of the team's decision if he's in the base game or not, and you will just have to accept it.
To be a little more fair here, Kart technically does... In that there are clearly anime-inspired characters in bonuschars (which almost all servers add), but they are all tied to video games (or in Miku's case, SEGA software first, video games later), so they still make sense as Kart characters. Sonic has never strayed that far from anime either, with Adventure 1's humans clearly leaning towards anime, and Sonic himself being in two of them, Classic and Modern. Sonic hanging with some anime-esque folks is no stretch, and no real problem.